Gas detector



June 16, 1959 MlcHAEL 2,891,164

GAS DETECTOR Filed Jan. 4. 1954 INVENTOR. P0414 Lee- M a/95 vBY flaw, awmwgg All: flr razelva'ys GAS DETECTOR Paul Lee Michael, Pittsburgh, Pa.,assiguor to Mine Safety Appliances Company, Pittsburgh, Pa., acorporalion of Pennsylvania This invention relates to portable apparatusfor detecting the presence and percentage of a particular gas in asample of a gas mixture, and more part cularly to apparatus which usesultraviolet energy to aid in the detection.

Most of the existing methods of gas analysis or detection fall into oneof the following three classes:

(1) Physical. or physico-chemical methods.

(2) Adaptations of the ordinary methods of chemical analysis-volumetricanalysis, etc.

(3) Colorimetric or nephelometric method.

A number of small portable detectors have been produced for practicingeach of the methods just mentioned, but all of them have disadvantages.The gas detector, which is the subject of this invention, overcomes manyof those disadvantages. For example, it is more sensitive to lower gasconcentrations than the hot filament type of gas detector and is nothandicapped by filament poisoning. It also can measure non-combustiblemixtures. The apparatus of this invention is not subject to excessivetime consumption or to special preparations needed for most chemicalmethods. Also, it is adaptable to more gases than present colorimetricdetectors and is not influence by sample flow. Finally, it does notrequire special preparations for each gas being analyzed.

In accordance with this invention, a housing has a window in one sidethat will filter out ultraviolet rays.

United States Patent The insideof the housing is provided with means forholding a thin strip of material, which is color-sensitive toultraviolet rays, close to the window. Inside of the housing a source ofultraviolet energy is spaced a considerable distance from the housingwindow in a position to direct its rays toward the strip to change itscolor. The strip preferably is long and wound on spools at oppositesides of the window. The housing is adapted to receive a gas sample inthe path of the rays between the energy source and strip. Colorstandards are exposed to view beside the housing Window for matchingwith the color of the strip after it has been exposed to the ultravioletrays for a predetermined period. The color standard that matches withthe color of the strip indicates the concentration of any of theultraviolet ray absorbing gas that is detected in the sample.

The preferred embodiment of the invention is illustrated in theaccompanying drawings, in which:

Fig. 1 is a plan view of my apparatus with part of the cover brokenaway;

Fig. 2 is a combined side view and vertical section; and

Fig. 3 is a cross section taken on the line IIL-III of Fig. 2.

Referring to the drawings, a rectangular housing is formed from an opentop box 1 that normally is closed by a snugly fitting cover 2. Thecover, preferably midway between its ends, is provided with arectangular opening, in which a window 3 is fitted. This window is madeof transparent material that will filter the ultraviolet rays out of thedaylight to keep such rays from entering the housing through the window.A suitable material for this purpose is a glass, No. 7380, manufacturedby Corning Glass Company.

In the upper portions of the opposite ends of the box, flanged spoolsare rotatably mounted in any suitable manner, such as like camera filmspools. The supply spool 5 contains a roll of thin strip material, suchas paper 6, the color of which will change when exposed to ultravioletrays. The outer end of this sensitive strip is pulled from the supplyspool and attached to the winding spool 7 at the opposite end of thehousing. The winding spool is provided with a knob 3 outside of thehousing for turning the spool in order to wind the strip on it asdesired.

An electrically operated source of ultraviolet energy 10 is mounted inthe housing below the sensitive strip 6 and a considerable distance fromthe housing window, toward which it directs its rays. A sample of thegas mixture to be analyzed for the purpose of determining whether acertain known gas is present in it, as well as the concentration of thatgas, is admitted to the housing. The gas being detected, which includesvapor, must be one that will absorb ultraviolet rays. Examples arehydrogen sulfide, carbon tetrachloride, ammonia, water vapor, benzine,carbon monoxide, ether, mercury vapor, etc. The ultraviolet rays fromsource 10 pass through a considerable portion of this sample beforereaching the sensitive strip. If the gas that is being detected ispresent, it will absorb ultraviolet energy in proportion to the amountof that gas in the sample. Thus, the greater the concentration of thegas in question, the more ultraviolet energy it will absorb and thelighter the color of the sensitive strip will appear. The color of thestrip is changed completely through it, so that the change can be seenthrough window 3.

Mounted on top of the housing cover on opposite sides of its window arecolor standards, which may be cards 12 and 13 of suitable materialdivided into sections show ing difierent shades of the color that thesensitive strip takes when exposed to ultraviolet rays. The color orshade of the exposed strip, as seen through the housing window,therefore can be compared with the color standards to match it with oneof them. The standards can be marked in percentages of gasconcentration, so that a direct reading of the gas concentration in thesample can be made.

The sensitive strip should be held close to the inner surface of window3 for good visibility, so means is provided for that purpose. This meanscan be part of means for keeping the gas sample from coming in contactwith the sensitive strip, which is desirable in. some cases, and forpreventing the sample from leaking out of the housing between the boxand cover. Accordingly, the housing contains a chamber to which the gassample is confined and by which the strip is held close to the housingwindow. This chamber may have a fiat bottom wall 15 spaced from thebottom of the box, and an upper wall formed from two plates 16 and 17extending from opposite ends of the box inward beneath the adjacentspools and then curving upward to points preferably close to theopposite edges of the housing window. Consequently, the spools arelocated in recesses formed between the top of the chamber and thehousing. The space between the upper ends. of the two curved plates isclosed by a window 18 that will transmit ultraviolet rays from source 10to the sensitive strip located between the two windows. The lower windowholds the strip close to the window above it. Although the two windowsare shown registering with each other, it is not necessary that they doso, in which case the strip would have to be moved from window 18 towindow 3 after exposure. Joined to one end of the sample chamber is aninlet tube 19 that extends out through the end wall of the housing,while a similar tube 20 is connected to the opposite end of the chamber.Any well known means may be used for pumping or drawing gas samples intoand out of the chamber through the two tubes.

With this construction it is preferred to provide the iiat'bottom wallof the gas chamber with a central rectangular opening sealed by anultraviolet ray transmitting glass 22. Directly below this glass thesource of ultraviolet energy is located. A curved reflector 23 extendsbeneath the source and helps to direct its rays upward through thechamber and window 18 to the sensitive strip.

To calibrate this instrument for a particular ultraviolet rayabsorbinggas, a sample of a reference gas containing a known concentration of rayabsorbing gas is delivered to the gas chamber. After passing ultravioletenergy from source through the gas for a predetermined time, such as 30or 40 seconds, the color of the sensitive strip as seen through window 3is matched with the color standards. The standard that matches the stripis marked with the percentage of the ultraviolet ray absorbing gas knownto be in the sample. By repeating this operation for various knownconcentrations, the apparatus is calibrated to read the concentration ofgas directly. It is notnecessary to change the color standards for eachdifierent gas that is to be detected, because several different gasesmay fall into a group that uses the same color standards.

Before operating the gas detector, it is necessary to stabilize'theultraviolet source by allowing it to warm up for a few minutes. A sampleof gas then is drawn into the gas chamber and the winding spool isturned to draw an unexposed area of the sensitive strip into the spacebetween the two windows. At the end of the prescribed exposure time, thepresence and concentration of a particular gas can be determined bycomparing the color of the strip with the color standards. Later a freshgas sample can be admitted to the chamber and the sensitive strip can bemoved to locate another unexposed area between the windows.

According to the provisions of the patent statutes, I have explained theprinciple of my invention and have illustrated and described what I nowconsider to represent its best embodiment. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically illustrated anddescribed.

I claim:

1. A gas detector for use in an atmosphere where it is known that onlyone ultraviolet ray absorbing gas may be present in an amount that canreadily be detected,

said detector comprising a housing provided in one side with a windowthat filters out ultraviolet rays, means in the housing adapted to holdclose to the window a thin strip of material color-sensitive toultraviolet rays, a constant source of ultraviolet energy in the housingspaced a considerable distance from said window in a position todirectits rays toward the strip to. change its color, said housing beingadapted to receive in the path of the rays between said energy sourceand strip, a gas sample that may contain acertain ultraviolet rayabsorbing gas, and color standards exposed to view beside the housingwindow for matching with the color of the strip after a predeterminedexposure period, whereby to indicate whether said ultraviolet rayabsorbing gas is present in the sample and its concentration therein.

2. A detector as defined in claim 1, in which said energy source islocated behind said window at the side of the housing opposite to thewindow.

3. A gas detector for use in an atmosphere where it is known that onlyone ultraviolet ray absorbing gas may be present in an amount that canreadily be detected, said detector comprising a housing provided with awindow in one side that filters out ultraviolet rays, a chamber in thehousing for receiving a gas sample that may contain a certainultraviolet ray absorbing gas, said chamber being provided in one sidewith an ultraviolet energy transmitting window adjacent said housingwindow, means for positioning outside of said chamber window a thinstrip of material color-sensitive to ultraviolet rays, a constant sourceof ultraviolet energy in a position to direct its rays through thechamber and its window to change the color of the strip, and colorstandards exposed to view beside the housing window for matching withthe color of said strip after a predetermined exposure time, whereby toindicate whether said ultraviolet ray absorbing gas is present in thechamber and its concentration therein.

References Cited in the file of this patent UNITED STATES PATENTS1,597,487

I St. Clair Aug. 24, 1926 1,997,356 Bryant Apr. 9, 1935 2,576,616Livingston et a1. Nov. 27, 1951 2,621,297 Obermaier Dec. 9,- 19522,624,011 Stern Dec. 30, 1952 2,680,816 Stein June 8,1954

